1. Field of the Invention
The present invention relates to a tubular membrane filtration module and, more particularly, it relates to a tubular membrane filtration module having a plurality of tubular permeable membranes suitable for treating raw liquids under a comparatively low pressure, such as ultrafiltration, microfiltration, etc.
2. Description of the Prior Art
Various permeable membranes, such as reverse osmosis membranes, ultrafiltration membranes, microfiltration membranes, etc. have been used for their selective permeability. Conditions for their use and the like are disclosed in, for example, U.S. Pat. Nos. 3,133,132, 3,526,588 and 3,567,810. Tubular membrane filtration modules equipped with these membranes have been widely used in many fields such as in the production of fresh water from sea water (desalination), condensation of colloids, treatment of waste liquor and the like as disclosed in, for example, various research and development reports issued by the Office of Saline Water (OSW), U.S.A.
In conventional tubular membrane filtration modules, the permeable membrane is supported by a porous FRP pipe as disclosed in, for example, Rozelle L. T. et al, Research & Development Report No. 531 by Office of Saline Water or a perforated stainless steel pipe as disclosed in, for example, S. Loeb, Desalination, 1, p35 (1966). These prior art tubular membrane filtration modules have a rather excessive quality which unnecessarily increases treatment costs. In the case of using these tubular membrane filtration modules under a comparatively low pressure, e.g., about 10 kg/cm.sup.2 G or less, such as for ultrafiltration or microfiltration, it is not necessary for the module to have such good pressure withstanding property.
Further, in the prior art tubular membrane filtration modules, the permeable membranes and the porous supporting pipes are sealed at the ends by means of packings, retainers or other sealing members as disclosed in, for example, Research & Development Report No. 993 by Office of Saline Water. However, the tubular permeable membranes are difficult to closely bundle using these members with the result that the area of membrane per unit volume of module is small. Further, the cross-sectional area of a flow passage in the module at the sealed portion is reduced and loss of pressure easily occurs which reduces the efficiency of the module and the flux through the membrane.
On the other hand, hollow fiber type (as disclosed in, for example, U.S. Pat. No. 3,228,876) or spiral type (as disclosed in, for example, U.S. Pat. No. 3,367,504) membrane filtration modules have been developed in order to improve the efficiency of the membrane filtration modules and, particularly, to increase the area of the membrane per unit volume of the module. However, these modules easily block and they are difficult to wash physically such as by using a sponge ball to remove scale deposits. Accordingly, in order to use such modules, it is necessary to pre-treat the raw liquid which in turn increases the cost. Furthermore, the above described membrane filtration modules are constructed of a large number of members such as permeable membrane supporting pipes, packings, retainers, headers, etc., and this makes them difficult to manufacture and expensive.